The present invention relates to automatic transmissions, and more specifically, to an adjustable pressure regulator for adjusting a hydraulic pressure in a hydraulic circuit of an automatic transmission.
In known automatic transmissions, such as the General Motors® Powerglide® automatic transmission, a hydraulic line pressure in the transmission is used to set the clamping force of clutch packs in the transmission. This line pressure can be changed to compensate for various factors relating to the vehicle configuration and use. In standard road use, such line pressures were set at the factory, generally were set in a range of 120-130 psi, and were never changed. Higher pressures provided more clamping force for the clutch packs and resulted in less likelihood of slippage through the clutch packs.
This transmission has been out of production since the early 1970's, but nonetheless continues to be very popular because of its consistency and simplicity and is still widely used in drag racing and some other off-road competitions. As the vehicles used in such drag racing are often extensively modified, and the vehicles are not used for any other purpose than drag racing, it is advantageous if the line pressure can be set to function best for the particular vehicle in which the transmission is to be installed. This involves considering several factors, including, among other things, horsepower/torque of the engine, weight of the vehicle and driveline drive ratios. The line pressure, for such racing application transmissions, is now generally set by the transmission rebuilder according to the factors noted above. The optimal setting of the hydraulic line pressure can vary from vehicle to vehicle, based on the above factors, and is desirably capable of fine tuning (fine adjustment) to optimize the setting for the vehicle. Powerglide® drag racing transmissions generally have line pressures set at between 140-230 psi to handle the greater torque transmitted through the transmission. While higher line pressures can be desirable to increase the holding power of the clutch packs, setting the pressure higher than is necessary for the specific vehicle wastes engine power that could otherwise be used to drive the vehicle forward. Thus, pressures that are set too high for the particular vehicle can decrease the performance of the vehicle by shunting propelling engine power to create unnecessarily high line pressures. Generally then, the specific vehicle performance will be maximized by setting the line pressure at the least pressure that will prevent clutch pack slippage for the specific vehicle. Setting the line pressure any higher wastes engine power that could otherwise be propelling the vehicle.
The Powerglide® transmission uses an elongated, axially movable line pressure valve to regulate line pressure in the transmission. Hydraulic fluid from the transmission pump is connected to a first end of the line pressure valve and creates a line pressure against the first end of the line pressure valve. A resistive force is applied to the opposing second end of the line pressure valve to resist this line pressure against the first end of the line pressure valve. The line pressure valve remains in a closed position by the resistive force until the line pressure against the first end of the line pressure valve overcomes the resistive force, whereupon the line pressure valve opens. The higher the resistive force, the higher the line pressure needed to overcome the resistive force. Thus, the line pressure can be adjusted by adjusting the resistive force.
The standard Powerglide® uses two components to set the resistive force, and thus, the line pressure. First, a replaceable boost sleeve and boost valve (piston) combination is connected to a hydraulic boost circuit of the transmission. The boost valve is slideably disposed in the boost sleeve and a first end of the boost valve is exposed to the hydraulic boost circuit. Depending on the pressure in the hydraulic boost circuit and the cross-sectional area of the first end of the boost valve, a resistive force is created on a second end of the boost valve, which engages the second end of the line pressure valve. For purpose of explanation, this resistive force will be called RFH.
In addition, the standard Powerglide® uses a mechanical spring positioned between the boost sleeve and a flange of the line pressure valve (which in practice, can also be some form of retaining ring engaging a circumferential groove in the line pressure valve) to apply a second resistive force against the line pressure valve. This second resistive force will be called RFS. The total resistive force RFTOT acting against the line pressure valve in a standard Powerglide® is thus RFTOT=RFH+RFS. This RFTOT can be adjusted by the racing transmission rebuilder by varying the size of the cross-sectional area of the first end of the boost valve (usually by replacing the boost sleeve and boost valve in matched pairs of varying boost valve areas), by altering the spring rate of the resistive spring and/or by altering the preload on the resistive spring by the use of fixed spacers used to pre-compress the resistive spring. Usually, various combinations of the above methods are used to set the line pressure to the desired level.
The automatic transmission will now be described in greater detail, with reference to the noted Figs. The automatic transmission 10, such as a Powerglide® transmission shown in FIG. 6, includes a valve body 12 (see also FIG. 2 (Prior Art)) in which a number of hydraulic fluid routing functions are performed. One such function is to control a line pressure valve 14 (see FIG. 1 (Prior Art)) to regulate hydraulic line pressure in the automatic transmission 10. As further shown in the exploded view of FIG. 1 (Prior Art), a conventionally known line pressure regulating system 16 includes a pressure regulating boost sleeve 18 (shown in a sectional view) in which a pressure regulating boost valve 20 is operationally disposed. The boost sleeve 18 includes a port (not shown in communication with a hydraulic boost circuit of the valve body 12 so that a first end 22 of the boost valve 20 is exposed to the hydraulic boost pressure in the pressure regulating boost sleeve 18. The boost valve 20 also includes a second end 24 for engaging a second end 28 of the line pressure valve 14. A first end 26 of the line pressure valve 14 is exposed to the hydraulic line pressure when installed in the valve body 12.
A spring retainer 30 engages the pressure regulating boost sleeve 18 and positions a pressure regulating spring 32 positioned between the spring retainer 30 and a retainer flange 34 of the line pressure valve 14. The retainer flange 34 can be machined or cast as part of the line pressure valve 14 or can be in the form of a retaining ring. A preload spacer 36 can be disposed between the pressure regulating spring 32 and the retainer flange 34. Altering the thickness of the preload spacer 36 alters the preload of the pressure regulating spring 32. A retaining ring 38 engages a circumferential slot in a valve bore 40 (see FIG. 2) of the valve body 12, to retain the pressure regulating system 16 in the valve bore 40.
The conventional line pressure regulating system operates in the following manner. First, the replaceable boost sleeve 18 and boost valve 20 combination is connected to the hydraulic boost circuit of the transmission. The boost valve 20 is slideably disposed in the boost sleeve 18 and the first end 22 of the boost valve 20 is exposed to the hydraulic boost circuit. Depending on the pressure in the hydraulic boost circuit and the cross-sectional area of the first end 22 of the boost valve 20, a resistive force is created on the second end 24 of the boost valve 20, which engages the second end 28 of the line pressure valve 14. This resistive force is RFH.
In addition, the mechanical spring 32 positioned between the spring retainer 30 and the flange 34 of the line pressure valve 14 applies a second resistive force against the line pressure valve, which is RFS. The total resistive force RFTOT acting against the line pressure valve 14 in a standard Powerglide® is thus RFTOT=RFH+RFS. This RFTOT can be adjusted by the racing transmission rebuilder by varying the size of the cross-sectional area of the first end 22 of the boost valve 20 (usually by replacing the boost sleeve 18 and boost valve 20 in matched pairs of varying boost valve areas), by altering the spring rate of the resistive spring 32 and/or by altering the preload on the resistive spring by the use of various thicknesses of preload spacers 36 to pre-compress the resistive spring 32. Usually, various combinations of the above methods are used to set the line pressure to the desired level.
The first end 26 of the line pressure valve 14 is exposed to the pressurized hydraulic fluid (from the transmission pump) in the line pressure circuit of the valve body 12. This hydraulic line pressure acts on the first end 26 of the line pressure valve 14 to create a valve opening force FVO that acts to open the line pressure valve 14 by moving it to the left (as seen in FIG. 2) in the valve body 12. However, this FVO is being countered by the RFTOT. Therefore, the line pressure valve 14 cannot open in the valve body 12 until the FVO has increased to be at, or above, the RFTOT, whereupon, the line pressure valve 14 opens, allowing excess line pressure to bleed off. Therefore, as is known, through this system the FVO will be regulated under normal operating conditions to a level of about that of the RFTOT, thereby also regulating the line pressure that corresponds to the FVO. Increasing the RFTOT, through one or more of the techniques noted above, thus increases the regulated line pressure, and correspondingly, decreasing the RFTOT, through one or more of the techniques noted above, decreases the regulated line pressure.
There are several disadvantages to the standard approach to regulating the line pressure in a Powerglide® transmission. First, the various components described above that can affect the line pressure cannot be readily removed and replaced in the valve body without removing either the transmission from the vehicle or the valve body from the transmission. This is time consuming and increases the chances of contamination and leakage of the valve body caused by the assembly and reassembly.
Second, a relatively large supply of varied boost sleeve/boost valve pairs, springs and spacers is needed to be able to create the correct combination to derive the desired line pressure. The finer the level of adjustability required, the greater the number of varied components that are needed to be able to derive the desire line pressure setting. This increases inventory costs for maintaining this supply of parts and also increases the complexity of determining the correct combination of parts to derive the desired line pressure. Such complexity can easily push adjustment of the line pressure beyond the capability of the vehicle owner, and prevent the vehicle owner from himself being able to fine tune the line pressure to his particular vehicle to maximize the performance of the vehicle. In fact, at the present time, adjustment of the line pressure in a Powerglide® transmission is not generally considered to be a vehicle owner task.
Further, it is known for the hydraulic portion of the resistive force to be problematic. That is, the boost valve is known to become jammed in the boost sleeve, often through contamination between the boost valve and boost sleeve, thereby either completely eliminating the hydraulic portion of the resistive force if the boost valve jams in a position away from the line pressure valve so that it does not contact the line pressure valve under normal movement of the line pressure valve (thereby leaving the line pressure too low) or by jamming in a position that prevents full movement of the line pressure valve (and thereby causing the line pressure to become higher than desired). This can seriously affect the performance, and even drivability, of the vehicle, and can also damage components of the transmission and vehicle. Resolving this problem requires, at the least, disassembly of the valve body to remove the contamination, and may require replacement of the boost sleeve/boost valve pair if either component has been damaged.